Misc. Haxe improvements

This is the second part of the Haxe addition started with THRIFT-2644, completing the base feature set with HTTP client and stream transports.

Test improvements

• added missing testException tests
• aligned cross test return codes
• aligned cross test command line arguments
• added --skip-speed-test switch

Code generator improvements

• added suffix "_FIELD_ID" to the fieldIDs to prevent name collisions with uppercase-only members (like ID, VAT)
• always render enum type with full namespace to prevent name collisions with class members

Library improvements

• HTTP transport client added
• Generic Stream transport added, implemented FileStream transport
• fixed possible double UTF-8 encoding/decoding in JSON protocol
• Haxe Thrift library test project added